Various kinds of insulation are used to provide thermal barriers on equipment, apparatus, buildings, vessels, tanks and other structures. One of the most useful types of insulation is produced by expanding through a spray nozzle a liquid mixture of two or more components which quickly react to form a polymeric foam. The resulting foam can be cut into slabs, blocks or other shapes and then applied to the object to be insulated. Alternatively, the foamed insulation can be applied directly in place by spraying the liquid mixture directly onto the surface to be insulated and letting it expand and solidify. Foaming in place is preferable when large surfaces are to be insulated since it eliminates extensive costly labor and provides a continuous insulating bed lacking, or having few, abutting joints through which air can flow.
When the foam is developed between two spaced apart opposing surfaces which limit expansion, such as is disclosed in Garis et al. U.S. Pat. No. 3,548,453 and Larsen U.S. Pat. No. 3,991,842 in insulating the vertical walls of cylindrical tanks, a uniform foam thickness can be readily obtained. Producing a uniformly thick foam bed on one surface, without use of a restraining means of some kind to limit foam expansion, is quite difficult. This is easily appreciated when it is noted that the liquid mixture applied to the surface generally expands from 5 to 30 times in volume before the solid foam is formed. Even though the two patents identified above show machine reciprocal spraying of the liquid composition to produce a vertical foam bed as a single layer, horizontal or sloped surfaces are generally foamed in place by a skilled workman. The work is exacting, tiring and costly. However, even an experienced sprayer is unable to deposit the foam evenly or of uniform thickness, which is not surprising since he has no way to determine immediately the liquid thickness except by judgment and experience. In addition, manual foam deposition on comparatively windy days is generally not possible because an operator is unable to simultaneously handle the foaming nozzle and a portable wind screen. A need accordingly exists for apparatus and methods which will permit the mechanical application of foamed in place insulation, particularly on horizontal or sloped surfaces, and even during relatively windy conditions.